Raman spectroscopy of carbon-coated LiCoPO sub(4) and LiFePO sub(4) olivines

• Published in: Journal of power sources 2011-08, Vol.196 (15), p.6433-6439
• Main Authors: Markevich, E, Sharabi, R, Haik, O, Borgel, V, Salitra, G, Aurbach, D, Semrau, G, Schmidt, MA, Schall, N, Stinner, C
• Format: Article
• Language: English
• Subjects: Carbon; Decomposition; Laser beams; Lasers; Nanocomposites; Nanomaterials; Nanostructure; Olivine
• ISSN: 0378-7753
• DOI: 10.1016/j.jpowsour.2011.03.059

The effect of laser power on the Raman spectra of two carbon-coated nano-powders of LiCoPO sub(4) and LiFePO sub(4) olivine cathode materials were investigated. In the ambient atmosphere at a moderate laser power, the phenomenon of the removal of the carbon coating layer from both samples was detected. The olivine structure of LiCoPO sub(4)-C powder therefore remains unchanged during the prolonged exposure to a 4.3 mW laser beam. The mild removal of the carbon layer makes it possible to analyze the details of the LiCoPO sub(4) structure in air without interference from carbon. LiFePO sub(4)-C powder, together with carbon layer gasification, undergoes oxidative decomposition by the oxygen with the formation of Li sub(3)Fe sub(2)(PO sub(4)) sub(3) and Fe sub(2)O sub(3), even at a laser power of 1 mW. Thus, care should be taken when measuring and interpreting the Raman spectra of this material both in air and in an inert atmosphere, as obvious decomposition of the LiFePO sub(4) olivine structure takes place even at a moderate power of the excitation laser. A comparative study of the stability of these two carbon-coated nano powders under laser beam irradiation and heating was carried out with the use of TGA-mass spectrometry. Gasification of the carbon coating layer from olivine nano-powders during Raman measurements. The olivine structure of LiCoPO sub(4)-C powder is stable during exposure to a laser beam. LiFePO sub(4)-C powder decomposes at the same conditions to form Li sub(3)Fe sub(2)(PO sub(4)) sub(3) and Fe sub(2)O sub(3).